About 15 yrs. ago I did just what you are thinking about, I found a shooter grade pre'64 M/70 and sent it to Randall Redman to be rebored/rechambered to .35 Whelen. It turned out great, it is my favorite hunting rifle, I can recommend Randall's work without reservation. He is one of the old time rebore men, his work is first class, turnaround and cost are reasonable.
